The invention relates to a drive unit, specifically for a motor vehicle, including an internal combustion engine, a transmission and a hydrodynamic retarder including a rotor and stator.
Such a drive unit is known from DE 37 13 580 C1.
Retarders are employed primarily in heavy vehicles to absorb the kinetic braking energy accruing notably in braking actions at high speed of travel (adaptation braking) and to convert it to heat. But retarders are suited well also for required sustained braking outputs, for instance at a constant speed of 30 km/h on an incline of 7%. Oil serves normally as the operating fluid. The heat transferred in the retarder to the operating fluid must be delivered, by means of a heat exchanger, to the coolant or ambient air.
The retarder described in U.S. Pat. No. 3,720,372 is integrated in the engine of the drive, permanently joined to the crankshaft and constantly flooded by the coolant of the cooling system. The rotor of the retarder serves as circulating pump, instead of utilizing a separate coolant pump. The purpose of this system is to cause heating of the coolant by means of the retarder for heating the passenger compartment. The same purpose serves also a control system arranged on the retarder, which controls merely the distribution of the coolant, depending on its temperature in a bypass line through the radiator.
Also known, from DE-PS 33 01 560, is a retarder which by way of a clutch is connected to the crankshaft of the drive engine and to the driven wheels of the vehicle. But the purpose of the retarder is not absorbing and converting high kinetic braking energy of the vehicle to heat. The retarder is operated exclusively as a heater, with the heating output meant to be controlled with a view to an available operating energy input. The coolant of the engine is likewise the operating fluid of the retarder.
A retarder described in DE-AS 1 946 167 (U.S. Pat. No. 3,650,358) is powered by the crankshaft of an internal combustion engine whose coolant serves also as operating fluid for the retarder. The advantage of this mode of operation is that the accruing heat develops directly in the coolant passed to the radiator and that a heat exchanger between two fluids is not needed. The rotor is mounted on an antifriction bearing and the seal between frame and rotor shaft is established by two lip seals.
The desire with drive units of this type is to keep the axial overall dimension and the weight as low as possible, especially when the drive unit is intended for a motor vehicle. With the drive units known heretofore, this was not achieved to a desirable degree.